1. Field of the Invention
The present invention relates to an adjusting device for a head rest provided on an automotive seat, and in particular to the improvement of fore-and-aft adjusting device for head rest basically comprising a shaped head rest stay whose lateral vertical leg portions are attached in the seat back and head rest mounted via a friction member on the hoizontal portion of the stay for allowing the forward and backward adjustment of the head rest relative to the seat.
2. Description of the Prior Art
A typical example of conventional head rest adjusting device using a friction means involves the one which employs a synthetic resin material for the frictional purpose as disclosed in the U.S. Pat. No. 3,695,700, in which a friction member of synthetic resin is wound about a head rest stay so that the head rest is angularly adjustable with the frictional effect of such friction member against the stay. This prior art has been found defective in that the friction member is not stable in its friction effect because of its high heat sensitivity resulting in the easy deformation under the changes of indoor temperature in the automobile and also under the frictional heat caused between the friction member and the stay, thus causing the difficulty of maintaining a constant frictional touch and control in the adjustment of the head rest.
Another type of the head rest adjusting device using a metallic friction means is known from the Japanese Utility Model Publication No. 60-36111, for instance, according to which its head rest frame is frictionally secured by a initially coned disc spring and small plate spring. But these friction means are contacted with the head rest frame in a small contact area, and consequently, there is no sufficient and stable frictional relationship between the friction means and head rest frame.